Transporting and storing temperature sensitive cargo over periods of time may require a controlled climate in the space where the cargo is loaded. Climate control includes controlling temperature of the cargo and humidity of air in the container to be within acceptable limits. Controlling the temperature includes bringing the temperature of the cargo into the acceptable range, by refrigerating or heating, and maintaining the temperature within that range. Climate control may also include controlling composition and humidity of the air in the space where cargo is loaded.
The temperature of temperature sensitive cargo should be kept within predefined acceptable limits. Some cargo must be maintained frozen, and the temperature of any portion of the frozen cargo must be kept below a predefined freezing temperature which depends on the cargo, e.g. below −18 degrees Celsius (i.e., 0.4 degrees Fahrenheit) or lower, while commodities such as fresh fruit and vegetables should be kept chilled, but not frozen, to stay fresh.
During operation of a refrigeration system water vapour will condense on the evaporator and form a layer of ice that will degrade the efficiency of the evaporator and thereby of the refrigeration system. Accumulated ice is removed by running a defrosting cycle. Traditionally, defrosting cycles are initiated according to a predetermined schedule at time intervals which may depend on the nature of the cargo and the time since its loading into the container, or defrosting can be performed on demand based on actual findings.
Some cargos need relative humidity to be kept within acceptable limits. Some cargos are sensitive to high or low temperatures, while others are relatively insensitive to temperature. Examples of such products are electronic and optical products, scientific instruments, machinery and metals such as iron and steel that may corrode if the relative humidity is too high, clothing and other textiles where fungus growth can be prevented by keeping the relative humidity low.
For temperature sensitive cargo such as chilled and frozen cargo it is of vital importance that the cargo is kept within an acceptable temperature range, since the cargo might otherwise deteriorate and become worthless.
It is therefore usual to perform a pre-trip inspection, PTI, of the container where structural and functional components of the container are inspected and tested with the purpose of ascertaining that the container will be able to function properly for at least one more journey with cargo.
A container with its cargo is delivered to its destination where the cargo is removed from the container. The empty container may then be transported to an inspection facility where a PTI is performed on the empty container. Containers which meet the quality criteria pass the PTI are approved for continued use for a certain period before a new PTI must be performed. This approval is documented in a satisfactory PTI report, which most insurance carriers require prior to shipment. Containers which do not meet the quality criteria do not receive a satisfactory PTI report and are not approved for continued use and appropriate action is therefore taken to restore the quality e.g. by repair or adjustment. Such procedure is time consuming.